A method is described in PCT Application No. WO 2015/120939 A1 in which, when a particular internal pressure is desired in a cavity of a micromechanical component or a gas mixture having a certain chemical composition is to be enclosed in the cavity, the internal pressure or the chemical composition is frequently adjusted during capping of the micromechanical component or during the bonding process between a substrate wafer and a cap wafer. During capping, for example, a cap is connected to a substrate, whereby the cap and the substrate together enclose the cavity. By adjusting the atmosphere or the pressure and/or the chemical composition of the gas mixture present in the surroundings during capping, it is thus possible to adjust the particular internal pressure and/or the particular chemical composition in the cavity.
With the aid of the method described in PCT Application No. WO 2015/120939 A1, an internal pressure may be adjusted in a targeted way in a cavity of a micromechanical component. It is in particular possible with the aid of this method to manufacture a micromechanical component including a first cavity, a first pressure and a first chemical composition being adjustable in the first cavity, which differ from a second pressure and a second chemical composition at the time of capping.
In the method for targeted adjusting of an internal pressure in a cavity of a micromechanical component according to PCT Application No. WO 2015/120939 A1, a narrow access channel to the cavity is created in the cap or in the cap wafer, or in the substrate or in the sensor wafer. Subsequently, the cavity is flooded with the desired gas and the desired internal pressure via the access channel. Finally, the area around the access channel is locally heated with the aid of a laser, the substrate material liquefies locally and hermetically seals the access channel during solidification.
In rotation rate sensors, for example, a very low pressure is enclosed, which is less than 1 mbar, for example. This is the case because a part of the movable structures is driven resonantly in rotation rate sensors. At low pressure, an oscillation may be excited very easily using relatively low stresses as a result of the slight damping.
In acceleration sensors, in contrast, it is not desirable for the sensor to begin to oscillate, which would be possible upon application of an external acceleration. The sensors are therefore operated at higher internal pressure. The internal pressure of an acceleration sensor is, for example, 500 mbar.